CVE-2025-40245 nios2: ensure that memblock.current_limit is set when setting pfn limits
A kernel panic occurs on nios2 systems with FLATMEM due to incorrect memory limit calculations, causing a denial of service.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2025-40245?
CVE-2025-40245 is a high-severity denial of service vulnerability in Linux, published on 4 Dec 2025. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
nios2: ensure that memblock.current_limit is set when setting pfn limits
On nios2, with CONFIG_FLATMEM set, the kernel relies on memblock_get_current_limit() to determine the limits of mem_map, in particular for max_low_pfn. Unfortunately, memblock.current_limit is only default initialized to MEMBLOCK_ALLOC_ANYWHERE at this point of the bootup, potentially leading to situations where max_low_pfn can erroneously exceed the value of max_pfn and, thus, the valid range of available DRAM.
This can in turn cause kernel-level paging failures, e.g.:
[ 76.900000] Unable to handle kernel paging request at virtual address 20303000 [ 76.900000] ea = c0080890, ra = c000462c, cause = 14 [ 76.900000] Kernel panic - not syncing: Oops [ 76.900000] ---[ end Kernel panic - not syncing: Oops ]---
This patch fixes this by pre-calculating memblock.current_limit based on the upper limits of the available memory ranges via adjust_lowmem_bounds, a simplified version of the equivalent implementation within the arm architecture.
Which versions are affected by CVE-2025-40245?
How do I fix CVE-2025-40245?
Apply the vendor's patch.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2025-40245 being exploited?
There is no known exploitation of CVE-2025-40245 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2025-40245, DEBIAN-CVE-2025-40245, GHSA-56rc-pfj3-9mx3, ROOT-OS-DEBIAN-11-CVE-2025-40245, ROOT-OS-UBUNTU-2404-CVE-2025-40245, UBUNTU-CVE-2025-40245.